Electromagnetic bursts sampling with the first 10 modules of the calorimeter 'WILLI'

The electromagnetic calorimeter 'WILLI' is designed for the spectroscopy of high energy muons coming from the cosmic rays which penetrate the atmosphere. Part of their energy is released in the lead plates of the device in subsequent radiative interactions and comes out as high energy protons or electron-positron pairs. This secondary particles initiate electromagnetic cascade in the 10 cm of lead (radiation length in lead is 0.56 cm) divided in ten 1 cm thick slabs. After each centimeter of lead path, the developing cascade is 'seen' by a scintillator plate (3 cm ME 114 plastic). From all 10 signals one can reconstruct the longitudinal development of the cascade, whose parametrization depends on the material (lead) and on the initiating particle energy. We finally come to the program of the irradiation probability which depends on the cross sections and on the energy spectrum of the muons. After a 6000 shower acquisition the method of fitting the theoretical curves was tested and certain limits of the experimental device were revealed, especially in the case of large showers. (author)